Manufacture of heat insulation material



l Patented May 16, 1944 purreo artisan Mnyrmacroae or near msrronmrennu.

name vv. Grelder and Roger a. MacArthur, Wyoming, tibio, assignors toThe Philip Carey Manufacturing @ompany, a corporation of Ohio NoDrawing.

Original application August 16,

1938, Serial No. 225,1i0. Divided and this application December 10,1940, Serialhlo. 3G$Ml32 11 claims.

This invention relates to the manufacture of molded heat insulatingmaterials. It relates es peciallyto the manufacture of molded heatinsulation materials utilizing normal magnesium carbonate. Thisapplication is a division of our application Serial No. 225,140filed'August 16, 1938..

In our co-pending application, Serial No.

225,139, filed August 16, 1938, we have disclosed that aqueous mixturesof normal magnesium carbonate and basic magnesium carbonate can bemolded substantially without drying shrinkage if the mixture is heatedto a temperature sufilciently high to convert the normal carbonate intobasic carbonate during or after molding and during or prior to drying.This property is of great economic importance in the manufacture ofmolded heat insulating materials.

Molded heat insulation materials are of diverse character. Onewell-known heat insulating ma terial is 85 per cent. magnesia whichconsists essentially of about 85 per cent. by weight of basic carbonateof magnesia and 15 per ,cent. by weight of asbestos fiber. Othersubstances such as calciumcarbonate, .diatomaceous earth, colloidalclays, mineral fibers, exfoliated vermiculite, and the like, maylikewise be admixed with basic carbonate of magnesia in the manufactureof molded heat insulation material.

In the manufacture of molded heat insulating materials, for example 85per cent. magnesia, a slurry of basic carbonate of magnesia in water isplaced in a-tank with air or other agitation and is mixed with asbestosfiber as a reinforcing means. The mixture is then pumped to storagetanks from which it is pumped under pressure to filter molds where apart of the water is ex-v pelled and the mass becomes sufiicientlycompacted for removal from the molds. These molds may be of variousshapes, depending upon the shape of insulating material beingmanufactured. For example, if slabs are to be made, the molds are ofrectangular cross section. If pipe covering is to bemade, the molds areof annular cross.

section. These molded rough shapes are commonly made considerably largerthan the finished shape which is to be made from the dried shape, asaccount must be taken of the drying shrinkage and the fact that thedrying shapes tend to warp. It is common practice in the manufacture of85 per cent. magnesia heat insulation, for example, that 30 per cent.ormore by weight oi'the dried shape, on the average, is trimmed citprior to sale and shipment of the material.

This trim must be returned to the mixing tanks.

The molded and wet shapes are placed. on sup ports, which, in turn, areplaced on trucks and placed in drying ovens. It is the function of the.supports to hold the wet shapes without collapse or excessivedeformation during the drying operation. These supports are usually madeof heavy wire mesh or perforated sheet metal and aside from theexpenseoi manufacture, must be constantly repaired and straightened atrelatively great expense.

As disclosed in our co-pending application, Serial No. 225,139, dryingshrinkage of molded heat insulation can be greatly reduced and evensubstantially entirely eliminated by the incorporation of finely-dividednormal magnesium carbonate crystals in an aqueous slurry of theingredients of the heat insulation prior to molding the same. Also, themolded articles, after being heated to a sufiiciently high temperaturefor a short period, set firmly, and become so hard and strong that theyneed no supports while drying.

In the use of this method, the molded articles.

may be placed on a table or conveyor, and subjected to temperatures offrom l3.'to 300 F. or over for a short period. They may then be removedand further dried without necessity for supports. molded closely to theexact dimensions wanted in the dried insulation as the drying shrinkageis virtually eliminated.

The basic magnesium carbonate used 'in the manufacture of molded heatinsulating materials is commonly prepared ;rom the mineral dolomite bywhat is known as the Pattinson process. In the practice of this method,dolomite rock, which is essentially an equi-molecular mixture of calciumcarbonate and magnesium carbonate of the approximate chemical formulaMgCOzCnCOa is first calcined, or burned, in a kiln to convert thecarbonate rock into a mixture of calcium oxide and magnesium oxide,essentially of the chemical formula MgO.CaO and called dolomitlc lime.This lime is then hydrated with water to form a dilute slurry of calciumand magnesium hydroxides, both substantially insoluble in water. Thisslurry is then treated by passing through it carbon dioxide-containinggas until all of the calcium hydroxide has been converted to insolublecalcium carbonate and substantially all of the magnesia is in the formof soluble magnesium bicarbonate oi the chemical formula: ivr mcom. Thesolid matter is then separated from the mixture of insoluble calciumcarbonate and soluble magnesium carbonate by filtration or settling orby a combination of these Also, the .molded articles may be tated. Thebasic carbonate is then available for use in the manufacture of moldedheat insulations, but the manufacture of molded insulation therefrom hasbeen attended with the excessive shrinkage during drying and the otherattendant disadvantages and difliculties that have been mentionedhereinabove.

Normal magnesium carbonate may be produced from a solution of magnesiumbicarbonate such as that occurring in the Pattinson process by-allowingthe solution to stand in air. However, the.

crystals of normal carbonate thus formed are too large and heavy to besuitable for use admixed with basic carbonate. Normal magnesiumcarbonate may also be prepared from bicarbonate solutions by treatmentwith soluble caustic alkalies, but these reagents are too expensive foruse in the commercial production of heat insulations.

Itis a purpose of this invention to avoid the difliculties due toexcessive shrinkage of molded insulations comprising basic magnesiumcarbonate, using magnesium bicarbonate solution such as that occurringin the Pattinson process as a source of magnesia. It is a furtherpurpose of this invention to recover normal megnesium carbonate frommagnesium bicarbonate solution by a simple and economical process and insuitable form for use in the manufacture of molded heat insulationmaterial.

We have discovered that normal magnesium carbonate of suitablecharacteristics for use in I the manufacture of heat insulationmaterials may be prepared commercially and economically from magnesiumbicarbonate solution such as that occurring in the Pattinson process bysub jecting the magnesium bicarbonate solution to a controlled heattreatment. Moreover, the heat treatment can be controlled so that partof the magnesium bicarbonate remains in the mother liquor and can beseparated from the precipitated normal carbonate. It is a furtherfeature of our method that magnesium bicarbonate remaining in the motherliquor can be converted into basic carbonate of magnesia by boiling themother liquor and that the basic carbonate of magnesia thus produced isavailable for combination with the normal magnesium carbonate producedas aforesaid and for use in the manufacture of molded heat insulationmaterial according to the method referred to hereinabove and describedin our said application, Serial No. 225,139, which inhibits dryingshrinkage. i

We have found that normal magnesium carbonate in suitable form can beprepared from a magnesium bicarbonate solution, e. g., the magnesiumbicarbonate solution occurring in the Pattinson process, if the solutionis heated to a temperature above about 140 F. and if the normalmagnesium carbonate that is formed is not exposed to a temperature aboveabout 158 F. for a sufilcient period of time to decompose it to basiccarbonate. The following are illustrative exam ples of the-practice ofthis invention.

A solution of magnesium bicarbonate of abou 3 per cent. concentration isfirst introduced continuously into a boiler, the contents of which areheld at a temperature of 158 F. or below by open steam introducedtherein. f Below F.,-insuiiicient velocity of decomposition occurs. Inthis boiler, normal magnesium carbonate crystals are formed and theheated slurry runs from the boiler continuously. The solid normalmagnesium carbonate in the withdrawn slurry is separated from theundecomposed bicarbonate methods well known to the art such as settlingor filtering or both. In a boiler operating as above disclosed, that is,at 140 F. to 158 F. and at atmospheric pressure, with a normal boilercycle of about 12 minutes (the time any given particle of solutionremains in the boiler), about 67 per cent. of the magnesia in thebicarbonate solution is recoverable as normal magnesium carbonate. Theundecomposed'solution is then transferred to a second boiler-where it isboiled at'a temperature above 190 F. and preferably above 200 F., untilsubstantially all of the remaining magnesium bicarbonate decomposes toform. basic magnesium carbonate. The normal magnesium carbonate from thefirst boiler may be washed if desired. It has been found possible tocontrol the particle size of the normal carbonate so' as to make theparticle size smaller in the final product by removing more or less ofthe mother liquor entrained in the paste as by washing the paste withwater. Agitation of the aqueous mass during the precipitation of thenormal magnesium carbonate also aids in the production of'fine crystalsof normal magnesium carbonate. The normal carbonate is then availablefor admixture with the basic carbonate formed as above disclosed.

By carrying on the operations above described at reduced pressure higheryields of normal magnesium carbonate can be obtained. Moreover, when thecontinuous boiling is carried on under reduced pressure, temperaturesabove 158 F. may be maintained provided the normal magnesium carbonateis not exposed to the higher temperature for a sufllciently long time toconvert the normal magnesium carbonatev into basic carbonate. Atemperature of about F. is the maximum that can be utilized practicallyin a continuous boiling operation even when the pres-- eration, thenormal magnesium carbonate is pro-- duced under the controlled heatingdescribed herein by heating magnesium bicarbonate solution to atemperature of about 140 F. to about 175 F., the normal magnesiumcarbonate not being exposed for a sufiicient period of time at thepressure under which it ismaintained to decompose it to the basiccarbonate. The process above described is particularly suited for acontinuous operation wherein the bicarbonate solution is introducedcontinuously into a heating chamber solution by and normal magnesiumcarbonate is continuous- 1y withdrawn from the heating chamber.

Normal magnesium carbonate may be Produced from magnesium bicarbonatesolution in the practice of this invention not only by a continuousboilingoperation as described above but also by a batch operation. Whenthe batch operation is practiced the formation of normal magnesiumcarbonate can be carried out not only within the temperature limitsabdve mentioned but also at higher temperatures provided the formationof the normal carbonate is initiated within the limits of temperatureand. pressure above described and We have found that ten minutes is asuitable time.

During this rapid heating the formation of normal magnesium carbonate isinitiated below 158 F. and continues at the higher temperatures, theyield of normal magnesium carbonate being high. The production of basiccarbonate is prevented by chilling the resulting slurry as by additionof cold water until the temperature of the mass is reduced to about 158F. or under and/or by washing the normal carbonate with water which isat a temperature below about 158 F. The yield in this case has beenfound to be about 90-92 per cent. of the magnesia in the magnesiumbicarbonate as normal carbonate. It is important that the solution beheated rapidly from less than about 158 F. to the maximum so that theformation of normal magnesium carbonate may be initiated below th stemperature inasmuch as this method of heating tends to prevent theformation of basic carbonate. The undecomposed magnesium bicarbonate inthe solution is separated from the precipitated normal carbonate and thenormal carbonate can be washed with water as above mentioned. Theseparated solution is subsequently boiled in the usual way to producebasic magnesium carbonate. The basic magnesium carbonate may then beused with normal magnesium carbonate produced as aforesaid in themanufacture of molded heat insulation materials in the manner abovedescribed.

If the batch process is carried out at reduced pressures a very highyield (nearly 100% of the magnes a in the magnesium bicarbonatesolution) can be obtained. Under reduced pressures the formation of thenormal carbonate can be instituted at temperatures above 158 F., e. g..at temperatures up to about 175 F. when a high vacuum is employed.Moreover, the normal magnesium carbonate does not have to be chilled to158 F. to prevent decomposition to normal carbonate so long as it ismaintained under acuum. However, when the normal carbonate is brought toatmospheric pressure it should be at a terrperature of 158 F. or less.By agtat ng the a ne ous mass during the precipitation of the normamagnesium carbonate the formation of fine crystals is promoted.

It is important to initiate the formation of normal magnesium carbonatein the batch process before the temperature is carried above that at whch the normal magnesium carbonate is stable for otherwise the magnesiumbicarbonate decomposes to form the basic magnesium carbonate as in thepreviously known Pattinson process.

;According to the foregoing procedure a step wise treatment of magnesiumbicarbonate solution such as that occurring in the Pattinson process ismade available whereby part of the magnesium bicarbonate is converted bya simple and economical treatment into normal magnesium carbonate whichis recovered and the balance of the magnesium bicarbonate is convertedinto basic magnesium carbonate which is also recovered. The normal andbasic carbonates may then be commingled in the manufacture of moldedheat insulation material with resultant inhibiting of drying shrinkageand great improvement upon the prior practice of merely using basicmagnesium carbonate such as that resulting from the Pattinson process asthe magnesia component of the molded heat insulation. While the normalmagnesium carbonate produced as aforesaid is advantageously combinedwith basic carbonate of magnesia obtained after separation of the normalmagnesium carbonate from its mother liquor, the normal magnesiumcarbonate can like wise be combined with basic magnesium carbonateobtained from other sources. Moreover, the special treatment ofmagnesium bicarbonate solution herein described in itself is to beregarded as a feature of this invention.

While this invention has been described hereinabov in connection withcertain examples of the practice of this invention, it is to be understood that this has been done merely to illustrate the practice of th sinvention and that the scope of this invention is to be governed by thelanguage of the following claims.

We claim:

1. A method of manufacturing molded heat insulation material whichcomprses heating magnesium bicarbonate solut on to precipitate normalmagnesium carbonate leaving part of the magnesium b carbonate in themother liquor, separating the normal magnesium carbonate from the motherliquor, heat ng the separated mother liquor sufficiently to convertmagnesium bicarbonate thereinto basic magnesium carbonate, making anaqueous slurry comprising normal magnesium carbonate produced asaforesaid and bas c magnesium carbonate produced as aforesaid, moldingthe slurry to form a molded art cle, and heating the molded articleprior to complete drying thereof sufficiently to convert normal magnesum carbonate therein into basic magnesium carbonate.

2. A method of manufacturing molded heat insulation material whichcomprises precipitating normal magnesium carbonate from a magnesiumbicarbonate solution at a temperature between about F., and about F.leaving part of the magnesium bicarbonate in the mother liquor. saidnormal magnesium carbonate not being ex posed for a sumcient period oftime at the pressure under which it is maintained to decompose it tobasic carbonate, separating the normal magnesium carbonate from themother liquor, heating the separated mother liquor sufficiently toconvert magnesium bicarbonate therein to basic magnesiumcarbonate,making an aqueous slurry comprising normal magnesium carbonate producedas aforesaid and basic magnesium carbonate produced as aforesaid,molding the slurry to form a molded article, and heating the moldedarticle prior to complete drying thereof sufiiciently to convert normalmagnesium carbonate therein into basic magesium carbonate.

3. A method of manufacturing molded heat insulation material whichcomprises heating magnesium bicarbonatesolution to a temperature aboveabout 140 F. under temperature and pressure conditions at which normalmagnesium carbonate is stable to initiate precipitation of normalmagnesium carbonate, then rapidly heating the normal magnesium carbonatethus' magnesium carbonate is unstable leaving. part of the magnesiumbicarbonate in the mother liquor and chilling the normal magnesiumcarbonate thus formed to a temperature at which the normal magnesiumcarbonate is stable before it decOmpOSes to basic carbonate, separatingthe normal magnesium carbonate from the mother liquor, heating theseparated mother liquor sufficiently to convert magnesium bicarbonatetherein to basic magnesium carbonate, making an aqueous slurrycomprising normal magnesium carbonate produced as aforesaid and basicmagnesium carbonate produced as aforesaid, molding the slurry to form amolded article, and heating the molded article prior to complete dryingthereof sufficiently to convert normal magnesium carbonate therein intobasic magnesium carbonate.

4. A method according to claim 3 wherein the rapid heating step iscarried to at least about 200 F, to form normal magnesium carbonate andthe normal magnesium carbonate thus produced is then rapidly chilled tobelow about 158 F. before it decomposes to basic carbonate.

5. A method of manufacturing molded heat insulation which comprisesheating magnesium bicarbonate solution to precipitate normal magnesiumcarbonate leaving part of the magnesium bicarbonate in the motherliquor, separating the normal magnesium carbonate from the motherliquor, heating the separated mother liquor sufiiciently to convertmagnesium bicarbonate therein bonate, forming an aqueous slurrycomprising I said mixed normal magnesium carbonate and basic magnesiumcarbonate, molding the slurry, and heating the molded material prior tocomplete drying to convert the normal magnesium carbonate to basicmagnesium carbonate.

8. A method of manufacturing magnesium carbonate which comprises heatingmagnesium bicarbonate solution at a temperature and pressure adapted toprecipitate normal magnesium carbonate leaving part of the magnesiumbicarbonate in the mother liquid, separating the precipitated normalmagnesium carbonate from the mother liquid, heating the separated motherliquid sufiiciently to convert magnesium bicarbonate thereinto basicmagnesium carbonate, and mixing said basic magnesium carbonate and saidnormal magnesium carbonate together.

9. A method of manufacturing magnesium carbonate which comprises heatingmagnesium bicarbonate solution at a temperature and pressure adapted toprecipitate normal magnesium carbonate leaving part of the magnesiumbicarbonate in the mother liquid, heating the separated mother liquidsufilcie'ntly to convert magnesium bicarbonate therein to basicmagnesium carbonate, mixing said basic magnesium carbonate and saidnormal magnesium carbonate together, and heating said mixed carbonatesin the presence of water to convert said normal magnesium carbonate tobasic magnesium carbonate while commingled with the previously formedparticles of basic magnesium carbonate.

10. -A method of manufacturing magnesium carbonate which comprisesheating magnesium bicarbonate solution at a temperature and pressureadapted to precipitate normal magnesium carbonate leaving part of themagnesium bicarbonate in the mother liquor, separating the nor-.

mal magnesium carbonate from the mother liouor, heating the separatedmother liquor suit!- to basic magnesium carbonate, mixing said basic manesium carbonate with normal magnesium carbonate, forming an aqueousslurry comprising said mixed basic magnesium carbonate and normalmagnesium carbonate, molding the slurry.

and heating the molded material prior to complete drying to convert thenormal magnesium carbonate into basic magnesium carbonate.

6. A method of manufacturing molded heat inulation which comprisesheating magnesium bicarbonate solution to precipitate normal magnesiumcarbonate, separating the normal magnesium carbonate from the motherliquor. mixing said normal magnesium carbonate with basic magnesiumcarbonate, forming an aqueous slurry comprising said mixed normalmagnesium carbonate and basic magnesium-carbonate, molding the slurry.and heating the molded material prior to complete drying to convert thenormal magnesium carbonate to basic magnesium carbonate.

7. A method of manufacturing molded heat in-' sulation which comprisesheating to at least about F. magnesium bicarbonate solution toprecipitate normal magnesium carbonate, separating the normal magnesiumcarbonate from the mother liquor, mixing said normal magnesium carbonatewith basic magnesium carciently to convert magnesium bicarbonate there--in to basic magnesium carbonate, mixing said basic magnesium carbonatewith normal magnesium carbonate, and heatingthe mixed carbonates in thepresence of water to convert the normal magnesium carbonate to basicmag-- nesium carbonate while commingled with the previously formedparticles of basic magnesium v carbonate.

11;. A method of manufacturing magnesium carbonate which comprisesheating magnesium bicarbonate solution at a temperature and pres sureadapted. to precipitate normal magnesium carbonate leaving part of themagnesium bicarbonate in the mother liquor, separating the normalmagnesiumcarbonate from the mother liquor, mixing said normal magnesiumcarbonate with basic magnesium carbonate produced by precipitation byrapid heating from a magnesium bicarbonate solution, .and heatingsaidmixed carbonatesin the presence of Water to convert said normalmagnesium carbonate to basic magnesium carbonate while commingled withthe previously formed particles of basic magnesium carbonate.

HAROLD W. GREIDER. ROGER A. MACART'HUR.

